Asystole and complete heart block detection

ABSTRACT

In one example, an apparatus of a wearable cardioverter defibrillator (WCD) system comprises a support structure wearable by a patient, a plurality of electrocardiogram (ECG) electrodes to obtain an ECG signal, a processor to receive and analyze the ECG signal of the patient, wherein the processor is configured to monitor four or more channels of the ECG signal, a high voltage subsystem coupled with defibrillation electrodes configured to be coupled with patient, wherein the processor is configured to cause the high voltage subsystem to apply a therapeutic shock to the patient through the defibrillation electrodes in response to a shockable event detected by the processor from the ECG signal. The processor measures a peak-to-peak amplitude of QRS complexes of the ECG signal, and detects asystole in the patient when the peak-to-peak amplitude of one or more QRS complexes is less than an asystole threshold. Other examples and related methods are disclosed herein.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. ProvisionalApplication No. 62/957,411 filed Jan. 6, 2020. Said Application No.62/957,411 is hereby incorporated herein by reference in its entirety.

BACKGROUND

When people suffer from some types of heart arrhythmias, the result maybe that blood flow to various parts of the body is reduced. Somearrhythmias may even result in a Sudden Cardiac Arrest (SCA). SCA canlead to death very quickly, for example within 10 minutes, unlesstreated in the interim.

Some people have an increased risk of SCA. Such people include patientswho have had a heart attack, or a prior SCA episode. A frequentrecommendation for these people is to receive an ImplantableCardioverter Defibrillator (ICD). The ICD is surgically implanted in thechest, and continuously monitors the patient's electrocardiogram (ECG).If certain types of heart arrhythmias are detected, then the ICDdelivers an electric shock through the heart.

As a further precaution, people who have been identified to have anincreased risk of an SCA are sometimes given a Wearable CardioverterDefibrillator (WCD) system, to wear until the time that their ICD isimplanted. Early versions of such systems were called wearable cardiacdefibrillator systems. A WCD system typically includes a harness, vest,belt, or other garment that the patient is to wear. The WCD systemfurther includes electronic components, such as a defibrillator andelectrodes, coupled to the harness, vest, or other garment. When thepatient wears the WCD system, the electrodes may make good electricalcontact with the patient's skin, and therefore can help sense thepatient's ECG. If a shockable heart arrhythmia is detected from the ECG,then the defibrillator delivers an appropriate electric shock throughthe patient's body, and thus through the heart. This may restart thepatient's heart and thus save their life.

WCD systems analyze the patient's ECG data as part of the determinationwhether to apply a therapeutic electric shock to the patient. WCDs aredesigned to detect and treat VT/VF, but they also may encounter patientswith extreme bradycardia and asystole. Current WCDs alarm and call forhelp when they encounter these rhythms but generally have no ability totreat those conditions. Furthermore, current WCDs generally are notcapable of distinguishing bradycardia and asystole from otherconditions.

DESCRIPTION OF THE DRAWING FIGURES

Claimed subject matter is particularly pointed out and distinctlyclaimed in the concluding portion of the specification. However, suchsubject matter may be understood by reference to the following detaileddescription when read with the accompanying drawings in which:

FIG. 1 is a diagram of components of an example wearable cardioverterdefibrillator (WCD) system in accordance with one or more embodiments.

FIG. 2 is a diagram of a back view of a garment of a WCD in accordancewith one or more embodiments.

FIG. 3 is a diagram illustrating four ECG monitoring vectors used in aWCD in accordance with one or more embodiments.

FIG. 4 is a diagram of ECG signals illustrating an asystole thresholdbased on peak-to-peak values of the detected QRS complexes in accordancewith one or more embodiments.

FIG. 5 is a diagram of ECG signals illustrating P-waves in addition toQRS complexes wherein P-wave morphologies are accounted for in detectedasystole in accordance with one or more embodiments.

FIG. 6 is a diagram of a method to detect asystole in a patient and todiscriminate asystole from fine ventricular fibrillation (VF) inaccordance with one or more embodiments.

FIG. 7 is a diagram of a method to detect complete heart block in apatient in accordance with one or more embodiments.

FIG. 8 is a diagram illustrating measurement of a respiration rate of apatient in accordance with one or more embodiments.

FIG. 9 is a diagram of detection of bradycardia in a patient using aconditional heart rate zone in combination with patient respiration inaccordance with one or more embodiments.

FIG. 10 is a diagram of detection of asystole in a patient using aconditional amplitude zone in combination with patient respiration inaccordance with one or more embodiments.

FIG. 11 is a diagram of discrimination between asystole and fineventricular tachycardia (VT) or ventricular fibrillation (VF) using aconditional amplitude zone in accordance with one or more embodiments.

FIG. 12 is a method to address asystole or bradycardia in a patientusing a wearable cardioverter defibrillator (WCD) in accordance with oneor more embodiments.

FIG. 13 is a diagram of the elements of a wearable cardioverterdefibrillator (WCD) using an external monitor to provide additionalpatient physiological parameter information to the WCD in accordancewith one or more embodiments.

It will be appreciated that for simplicity and/or clarity ofillustration, elements illustrated in the figures have not necessarilybeen drawn to scale. For example, the dimensions of some of the elementsmay be exaggerated relative to other elements for clarity. Further, ifconsidered appropriate, reference numerals have been repeated among thefigures to indicate corresponding and/or analogous elements.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth to provide a thorough understanding of claimed subject matter. Itwill, however, be understood by those skilled in the art that claimedsubject matter may be practiced without these specific details. In otherinstances, well-known methods, procedures, components and/or circuitshave not been described in detail.

In the following description and/or claims, the terms coupled and/orconnected, along with their derivatives, may be used. In particularembodiments, connected may be used to indicate that two or more elementsare in direct physical and/or electrical contact with each other.Coupled may mean that two or more elements are in direct physical and/orelectrical contact. Coupled, however, may also mean that two or moreelements may not be in direct contact with each other, but yet may stillcooperate and/or interact with each other. For example, “coupled” maymean that two or more elements do not contact each other but areindirectly joined together via another element or intermediate elements.Finally, the terms “on,” “overlying,” and “over” may be used in thefollowing description and claims. “On,” “overlying,” and “over” may beused to indicate that two or more elements are in direct physicalcontact with each other. It should be noted, however, that “over” mayalso mean that two or more elements are not in direct contact with eachother. For example, “over” may mean that one element is above anotherelement but not contact each other and may have another element orelements in between the two elements. Furthermore, the term “and/or” maymean “and”, it may mean “or”, it may mean “exclusive-or”, it may mean“one”, it may mean “some, but not all”, it may mean “neither”, and/or itmay mean “both”, although the scope of claimed subject matter is notlimited in this respect. In the following description and/or claims, theterms “comprise” and “include,” along with their derivatives, may beused and are intended as synonyms for each other.

Referring now to FIG. 1 , a diagram of components of an example wearablecardioverter defibrillator (WCD) system in accordance with one or moreembodiments will be discussed. A wearable cardioverter defibrillator(WCD) system 100 according to embodiments may protect an ambulatorypatient 110 by electrically restarting his or her heart if needed. Sucha WCD system 100 may have a number of components. These components canbe provided separately as modules that can be interconnected, or can becombined with other components, and so on.

FIG. 1 depicts a patient 110. Patient 110 may also be referred to as aperson and/or wearer since the patient is wearing components of the WCDsystem 100. Patient 110 is ambulatory, which means that, while wearingthe wearable portion of the WCD system 100, patient 110 can walk aroundand is not necessarily bed-ridden. While patient 110 also can beconsidered a “user” of the WCD system 100, this is not a requirement.For instance, a user of the wearable cardioverter defibrillator (WCD)may also be a clinician such as a doctor, nurse, emergency medicaltechnician (EMT) or other similarly tasked individual or group ofindividuals. In some cases, a user may even be a bystander. The contextof these and other related terms within this description should beinterpreted accordingly.

A WCD system 100 according to embodiments can be configured todefibrillate the patient 110 who is wearing the designated parts the WCDsystem 100. Defibrillating can be by the WCD system 100 delivering anelectrical charge to the patient's body in the form of an electricshock. The electric shock can be delivered in one or more pulses.

FIG. 1 also depicts components of a WCD system 100 made according toembodiments. One such component is a support structure 112, or garment,that is wearable by ambulatory patient 110. Accordingly, supportstructure 112 is configured to be worn by ambulatory patient 110 for atleast several hours per day, and for at least several days, even a fewmonths. It will be understood that support structure 112 is shown onlygenerically in FIG. 1 , and in fact partly conceptually. FIG. 1 isprovided merely to illustrate concepts about support structure 112, andis not to be construed as limiting how support structure 112 isimplemented, or how it is worn.

Support structure 112 can be implemented in many ways. For example, itcan be implemented in a single component or a combination of multiplecomponents. In embodiments, support structure 112 can include a vest, ahalf-vest, a garment, and so on. In such embodiments such items can beworn similarly to analogous articles of clothing. In embodiments,support structure 112 can include a harness, one or more belts orstraps, and so on. In such embodiments, such items can be worn by thepatient around the torso, hips, over the shoulder, and so on. Inembodiments, support structure 112 can include a container or housing,which optionally can be waterproof. In such embodiments, the supportstructure 112 can be worn by being attached to the patient's body byadhesive material, for example as shown and described in U.S. Pat. No.8,024,037 which is incorporated herein by reference in its entirety.Support structure 112 can be implemented as described for the supportstructure of U.S. application Ser. No. 15/120,655, published as US2017/0056682 A1, which is incorporated herein by reference in itsentirety. In such embodiments, the person skilled in the art willrecognize that additional components of the WCD system 100 can be in thehousing of a support structure instead of being attached externally tothe support structure, for example as described in the US 2017/0056682A1 document. There can be other examples.

FIG. 1 shows a sample external defibrillator 118. In some embodiments,external defibrillator may be referred to as a carry pack since thecomponents of external defibrillator can be contained in an externalpackage that is carried by the patient 110, for example using a shoulderstrap. As described in more detail later in this document, some aspectsof external defibrillator 118 include a housing and an energy storagemodule within the housing. As such, in the context of a WCD system 100,defibrillator 118 is sometimes called a main electronics module. Theenergy storage module can be configured to store an electrical charge.Other components can cause at least some of the stored electrical chargeto be discharged via electrodes through the patient to deliver one ormore defibrillation shocks through the patient 110.

FIG. 1 also shows sample defibrillation electrodes 104 and 108, whichare coupled to external defibrillator 100 via electrode leads 105.Defibrillation electrodes 104 and 108 can be configured to be worn bypatient 110 in several ways. For instance, defibrillator 100 anddefibrillation electrodes 104 and 108 can be coupled to supportstructure 112, directly or indirectly. In other words, support structure112 can be configured to be worn by an ambulatory patient 110 tomaintain at least one of electrodes 104 or 108 on the body of ambulatorypatient 110, while patient 110 is moving around, and so on. Theelectrode can be thus maintained on the body by being attached to theskin of patient 110, simply pressed against the skin directly or throughgarments, etc. In some embodiments the electrode is not necessarilypressed against the skin, but becomes biased that way upon sensing acondition that could merit intervention by the WCD system 100. Inaddition, many of the components of defibrillator 118 can be consideredcoupled to support structure 112 directly, or indirectly via at leastone of defibrillation electrodes 104 and/or 108.

When defibrillation electrodes 104 and 108 make good electrical contactwith the body of patient 110, defibrillator 118 can administer, viaelectrodes 104 and 108, a brief, strong electric pulse 111 through thebody. Pulse 111 is also known as shock, defibrillation shock, therapy,electrotherapy, therapy shock, etc. Pulse 111 is intended to go throughand restart heart 85 to save the life of patient 110. Pulse 111 canfurther include one or more pacing pulses of lesser magnitude to simplypace heart 85 if needed, and so on.

A typical defibrillator can decide whether to defibrillate based on anelectrocardiogram (ECG) signal of the patient. External defibrillator118, however, may initiate defibrillation, or hold-off defibrillation,based on a variety of inputs, with the ECG signal merely being one ofthese inputs.

A WCD system 100 according to embodiments can obtain data from patient110. For collecting such data, the WCD system 100 may optionally includea hub or monitoring device 114. Device 114 is can be provided as astandalone device, for example not within the housing of defibrillator118. Device 114 can be configured to sense or monitor at least one localparameter. A local parameter can be a parameter of patient 110, or aparameter of the WCD system 100, or a parameter of the environment, aswill be described later in this document. In some embodiments,monitoring device 114 can comprise or be referred to as a hub or similardevice through which connections and/or leads may be made of the variouscomponents of the WCD system 100. For example, at least some of theleads of external defibrillator 118 may be connected to and/or routedthrough the monitoring device 114 including, for example, one or moreECG leads, a right-leg drive (RLD) lead, leads connected to thedefibrillation electrodes 104 and/or 108, and so on. In someembodiments, monitoring device 114 can include a controller or processorthat is used to implement at least a portion of the shock/no-shockalgorithm to determine whether a shock should or should not be appliedto the patient 110, although the scope of the disclosed subject matteris not limited in this respect.

For some of these parameters, device 114 can include one or more sensorsor transducers. Each one of such sensors can be configured to sense aparameter of patient 110, and to render an input responsive to thesensed parameter. In some embodiments the input is quantitative, such asvalues of a sensed parameter. In other embodiments the input isqualitative, such as informing whether a threshold is crossed, and soon. Sometimes these inputs about patient 110 are also calledphysiological inputs or patient inputs. In embodiments, a sensor can beconstrued more broadly, as encompassing many individual sensors.

Optionally, device 114 can be physically coupled to support structure112. In addition, device 114 may be communicatively coupled with othercomponents that are coupled to support structure 112. Such communicationcan be implemented by a communication module, as will be deemedapplicable by a person skilled in the art in view of this description.

In embodiments, one or more of the components of the shown WCD system100 may be customized for patient 110. This customization may includeseveral aspects. For instance, support structure 112 can be fitted tothe body of patient 110. For another instance, baseline physiologicalparameters of patient 110 can be measured, such as the heart rate ofpatient 110 while resting, while walking, motion detector outputs whilewalking, etc. The measured values of such baseline physiologicalparameters can be used to customize the WCD system 100 to make itsdiagnoses more accurate, since patients' bodies differ from one another.Of course, such parameter values can be stored in a memory of the WCDsystem 100, and so on. Moreover, a programming interface can be madeaccording to embodiments, which receives such measured values ofbaseline physiological parameters. Such a programming interface mayinput automatically in the WCD system 100 these values along with otherdata

In one or more embodiments, WCD system 100 can include an externalmonitor 150 that is capable of monitoring various physiologicalparameters of the patient. For example, external monitor 150 cancomprise a non-invasive blood pressure (NIBP) monitor to measure theblood pressure of the patient 110 as one or more of the patientparameters collected by WCD system 100. In another example, externalmonitor 150 can comprise a pulse oximeter to measure the oxygensaturation of the patient 110. In yet another example, external monitor150 can measure the heart rate of the patient 110 independent from theECG signal obtained by hub/monitoring device 114. Monitoring device 150can be configured to combine multiple functions to take multiple typesof physiological parameter measurements of the patient 110, and thescope of the disclosed subject matter is not limited in these respects.Furthermore, external monitor 150 can obtain frequent measurements ofone or more physiological parameters while the patient 110 is wearingthe monitor through the day and/or during the night when the patient 110is sleeping.

The external monitor 150 can be provided in various types of formfactors to be placed on the patient's body at various locations and/orto integrate with WCD system 100 in various ways. For example, in someembodiments, external monitor 150 may be worn on the wrist of thepatient 110 or various other locations on the patient 110 such as on thearm, leg, ankle, chest, or back of the patient 110 depending on theprovided form factor and/or technology utilized by the external monitor150 to obtain a physiological parameter reading.

In some embodiments, external monitor 150 may be incorporated into anexternal device or accessory such as a smartphone that employ varioussensors. Such devices may come in various other form factors such as apatch, watch, earring, eyeglasses, ankle bracelet, and so on, whereinthe external monitor 150 can be unobtrusive and in location in which thepatient's vasculature may be near the skin so that an optical sensor ofexternal monitor 150 can obtain good readings.

In some embodiments, external monitor 150 can include a sensor builtinto the alert button or stop button 120 (see FIG. 2 ) of the WCD system100 wherein the alert button or stop button 120 is used by the patient110 to stop an impending shock if the patient so desires. In suchembodiments, the patient 110 is already aware of the location of thealert button or stop button 120 which would provide a simple and readilyavailable device for the patient to use to take a measurement such asblood pressure and/or heart rate. In addition, when the external monitor150 is in the alert button or stop button 120, the patient's bloodpressure and/or heart rate can be obtained whenever the patient 110needs to abort a shock.

As previously mention, in one or more embodiments, the external monitor150 can include or otherwise comprise an optical pulse oximetry sensorand/or a methemoglobin sensor. In other embodiments, external monitor150 can be incorporated in one or more of the ECG electrodes of the WCDsystem 100. Such a sensor can be an optical sensor as described above,or an electro-mechanical sensor such as described in “A CMOS-basedTactile Sensor for Continuous Blood Pressure Monitoring”, Kirstein,Sedivy, et al., Proceedings of the Design, Automation and Test in EuropeConference and Exhibition, 1530-1591/05 (March 2005) which isincorporated herein by reference in its entirety.

In other embodiments, the external monitor 150 can be adapted for use inproposed adhesive type defibrillators as disclosed in U.S. Pat. No.8,024,037. For example, the external monitor 150 can be disposed in oneof the adhesive modules as shown in the '037 patent, or in an“appendage” or “flap” that extends from the module so that the externalmonitor 150 is positioned on an appropriate location on the patient.Embodiments of a cuff-less NIBP sensor can include a wirelesscommunication interface such as BLUETOOTH, near-field communication(NFC), Wi-Fi DIRECT, ZIGBEE, and so on, to transmit the blood pressuredata to a module of the WCD system 100, to a personal communicationdevice of the WCD system 100 for example as disclosed in U.S. Pat. No.8,838,235, or to another remote device. Said U.S. Pat. No. 8,838,235 isincorporated herein by reference in its entirety. In some embodiments, awired communication link can be used instead of a wireless communicationlink. For example, the external monitor 150 can be implemented in anelectrode that can be configured so that the physiological parameterdata is transmitted on a wire bundled with the wire or wires of theelectrode sensors, or multiplexed on the same wire as the electrodedata, and so on.

Referring now to FIG. 2 , a diagram of a back view of a garment of a WCDin accordance with one or more embodiments will be discussed. Thegarment shown in FIG. 2 can comprise the support structure 112 of FIG. 1and is shown in a vest configuration. The garment can include shoulderstraps 210 and 212 to be placed over the shoulders of the patient 110and for support of the support structure 112. The garment may include abelt portion 214 to be fastened around the waist of the patient 110. Thebelt portion 214 may include various fasteners 216 and 218, for exampleclosure snaps, to allow the garment to be fitted to different sizedusers. Hub/monitoring device 114 can be attached to the back side of thegarment, for example on or near the belt portion 214, to allow variouscables to be connected to hub 114 including alert button (or divertbutton or stop button) 120 and cabling to connect to thetherapy/defibrillator electrodes and ECG electrodes (not shown). In someembodiments, support structure 112 can comprise a vest-like fabricgarment to be worn on the patient's body underneath an outer shirt orother clothing to allow the electrodes to contact the patient's skin andhold the electrodes near and/or in direct contact with the patient'sskin. Such an arrangement allows for the WCD system 100 to obtain ECGsignals from the patient 110 and to allow the shock 111 to be applied tothe patient 110 when appropriate.

Referring now to FIG. 3 , a diagram illustrating four ECG monitoringvectors used in a WCD in accordance with one or more embodiments will bediscussed. As shown in FIG. 3 , patient 110 can wear support structure112 that can include ECG electrodes such as electrode (E1) 122,electrode (E2) 124, electrode (E3) 126, and electrode (E4) 128 atvarious locations around the patient's torso to obtain ECG signals fromthe patient 110. Support structure 112 can also include a right legdrive (RLD) electrode 130 as a reference for differential signals. Insome embodiments, the ECG signals obtained by WCD system 100 can bedigitized, and the digitized ECG signals can be referenced to anisolated ground of the ECG front end circuitry. Differential vectors canbe formed by subtracting two digitized ECG signals. ECG rhythm analysisthen can be performed on these four vectors. Such differential vectorsmay include, for example, vector (E24) 310, vector (E34) 312, vector(E12) 214, and vector (E13) 216. The defibrillator shock 111 may begenerated between the anterior defibrillation pad 104 and the posteriordefibrillation pad 108. The ECG analysis algorithm includes provisionsfor excluding vectors that have noise or when a leads-off condition orsituation is detected. Monitoring four vectors rather than monitoringtwo vectors is believed to contribute to enhanced ECG signal analysisand processing of the shock application algorithm to reduce the numberof false shock events.

In some embodiments, the signals from four ECG electrodes can becombined to form up to six different vectors. In some embodiments, WCD100 uses four vectors for QRS complex analysis and/or heart rateanalysis to determine if a shock should be applied. The WCD 100 is alsocapable of performing the analysis and shock application determinationif one or more of the vectors is noisy or one or more of the ECG leadsis in a lead-off condition wherein the lead is not contacting thepatient's skin or is not sufficiently contacting the patient's skin toallow an ECG signal to be obtained with that ECG lead. In someembodiments, three ECG electrodes may be used and three ECG vectors maybe analyzed. In other embodiments, five or six ECG vectors may beanalyzed using four ECG electrodes. In some embodiments, a single vectoris used and analyzed. It should be noted that in general WCD system 100may use and analyze fewer than four vectors or greater than fourvectors, and the number of vectors can be increased beyond six vectorsby using additional ECG electrodes, and the scope of the disclosedsubject matter is not limited in this respect.

In one or more embodiments as shown in FIG. 3 , the ECG electrodes canbe placed circumferentially around the torso of the patient 110 so thatthe garment or support structure 112 can be used to ensure adequateelectrode-skin contact with the patient's skin. It should be noted thatother alternative electrode placements may be used, and the scope of thedisclosed subject matter is not limited in this respect. For example,adhesive electrode embodiments can provide flexibility in electrodeplacement in selected locations of the patient's body and may achievebetter signal pickup at these selected locations. For example, electrodelocations can be selected during a patient-fitting process in whichvarious electrode locations can be changed, and those locations withbetter or the best ECG signals can be selected, although the scope ofthe disclosed subject matter is not limited in this respect.

In one or more embodiments, WCD system 100 can be configured to detectasystole and non-perfusing bradycardia in patient 110. The WCD system100 can be configured to non-invasively detect asystole and/ornon-perfusing bradycardia. In some embodiments, WCD system 100 cab beconfigured to provide external pacing as a therapy for detected asystoleand/or non-perfusing bradycardia. In some embodiments, asystole can bedetected simply by the absence of QRS complexes which is a flatline ECG(see FIG. 4 below). In some embodiments, WCD system 100 can beconfigured to analyze ECG signals on multiple vectors to confirm thatQRS complexes are not present on any of the available vectors. The WCDsystem 100 may check vectors that are not normally used before renderingan asystole decision. If the patient is in asystole, all vectors shouldhave a flatline ECG. In some embodiments, the WCD system 100 can beconfigured to detect whether the ECG leads that have an electrode off ordiscernable noise, and in response to such detection can exclude thesignals from those ECG leads from consideration for asystole detection.

In accordance with one or more embodiments, asystole can be detectedwith greater certainty by analyzing more than two vectors. WCD system100 can utilize four ECG electrodes to generate up to six ECG vectors.If all vectors are analyzed, then there is less chance that alow-amplitude rhythm may be mistaken for asystole.

FIG. 3 shows the relationship between physical electrode placement andECG vectors for an example WCD embodiment. The ECG electrode (E1) 122,electrode (E2) 124, electrode (E3) 126, and electrode (E4) comprisesingle-ended monitored electrodes. In some embodiments the right legdrive (RLD) electrode 130 can be used to manage common mode noise.Vector (E24) 310, vector (E34) 312, vector (E12) 314, and vector (E13)316 are the differential vectors that are derived from the single-endedvectors. Embodiment of how the ECG signals and vectors obtained with WCDsystem 100 can be used to detect asystole and non-perfusing bradycardiaare discussed below.

Referring now to FIG. 4 , a diagram of ECG signals illustrating anasystole threshold based on peak-to-peak values of the detected QRScomplexes in accordance with one or more embodiments will be discussed.Asystole can refer to the absence of ventricular contractions due tototal cessation of electrical activity in the heart such that the heartdoes not contract. When there is no heart contraction, there is no bloodflow in the patient 110. The patient's ECG signal will be a completeflatline. Sometimes it can be difficult to distinguish between asystoleand fine ventricular fibrillation (VF) which refers to a chaotic heartrhythms having very small amplitudes. In one or more embodiments, anamplitude threshold can be used to separate fine VF from asystole. Forexample, if the peak-peak value of an ECG signal is greater than 100microvolts (μV) then it can be classified as fine VF while a signal lessthan 100 μV would be classified as asystole. It should be noted thatfine VF can be a shockable condition whereas asystole would not betreated with a shock. As a result, WCD 100 can be configured todistinguish between fine VF with low-amplitude QRS complexes andasystole with no QRS complexes.

Plot 400 illustrates voltage versus time of a normal ECG signal 410. QRScomplexes 412 are shown in ECG signal 410 but p-waves and t-waves areomitted for purposes of example. A normal QRS complex 412 can have apeak-to-peak value 414 of up to about 2.5 millivolts (mV) or 3.0 mV. Incontrast to the normal ECG signal 410 shown in plot 400, plot 402 showsan ECG signal 416 having no QRS complexes and therefore there is nopeak-to-peak signal 414. Such an ECG signal 416 can be referred to as aflatline which indicates asystole.

Plot 404 shows an ECG signal 418 with QRS complexes 420 having lowpeak-to-peak values 414. Such low-amplitude QRS complexes 420 can bedifficult to distinguish from asystole. In one or more embodiments, anamplitude threshold 424 can be used to distinguish between low-amplitudeQRS complexes and asystole. The threshold can be for example about 100μV, although the scope of the disclosed subject matter is not limited inthis respect. As can be seen in plot 404, the peak-to-peak amplitude 422of QRS complexes 420 is less than the threshold 424. As a result, theseQRS complexes 420 can be classified as asystole. The peak-to-peakamplitude 428 of QRS complex 426 is greater than the threshold 424. As aresult, QRS complex 426 can be classified as fine VF.

WCD system 1000 can also utilize other techniques to avoid unnecessarymisclassifications of ECG signals. For example, in multichannelembodiments such as a multichannel arrangement of electrodes shown inFIG. 3 , the amplitudes of some channels may be different from otherchannels. A patient 110 wearing the multichannel device withlow-amplitude QRS complexes may be above the threshold 424 on somechannels but below the threshold 424 on other channels. In suchembodiments, a patient 110 can be determined to as asystolic only if thepeak-to-peak amplitudes of the QRS complexes on all channels are belowthe threshold amplitude. Otherwise, in some examples the patient can bedetermined to have fine VF.

In some embodiments, the threshold 424 can be adjustable for eachpatient 110. For example, the threshold 424 can be selected when thepatient 110 is fitted with a garment type support structure 112. Thepatient 110 is known to not be asystolic at that time, so a thresholdcould be chosen that is a fraction of the peak-to-peak QRS amplitude foreach channel, for example the threshold 424 can be set as 25% of thepeak-to peak amplitude of normal QRS complexes for each channel. Thus,some channels can have thresholds 424 below 100 μV, while other channelsmay have higher thresholds 424. In some embodiments, the WCD system 100can be configured with a maximum asystole threshold, for example 200 μVin some embodiments, regardless of the patient's actual QRS amplitude.In some embodiments, during the fitting process the patient 110 can beasked to lie down while the QRS amplitudes are measured, since a patientexperiencing asystole may be unconscious and lying down, with thethresholds 424 being selected using these QRS amplitude measurements.

It should be noted that QRS amplitudes can vary with patient posture.QRS amplitudes have been seen that can vary by about 50% over time on asingle vector in normal, healthy patients. As a result, in someembodiments the asystole threshold 424 can be set so that it is lowenough to avoid being crossed by the normal QRS amplitude variations. Insome embodiments, the thresholds 424 can be set for different patientpostures. In a further embodiment, the WCD system may include a sensorfor determining the patient's posture, with the threshold 424 beingdynamically adjusted based on the determined posture. For example,patient posture may be detected as disclosed in U.S. patent applicationSer. No. 15/863,551 entitled “WEARABLE CARDIOVERTER DEFIBRILLATOR HAVINGADJUSTABLE ALARM TIME” filed on Jan. 5, 2018, which is incorporated byreference in its entirety for all purposes.

In some embodiments, the asystole threshold 424 can be adjusted duringthe normal wear time by the patient 110. For example, if a patient 110receives an asystole alert and presses the alert/stop/response button120 which is used in WCD system 100 to indicate the patient 110 isconscious and thus should not be shocked, the WCD system can configuredto take this stop button 120 actuation as an indication that the patient110 is not in asystole and that the asystole thresholds 424 should beadjusted accordingly.

Referring now to FIG. 5 , a diagram of ECG signals illustrating p-wavesin addition to QRS complexes wherein P-wave morphologies are accountedfor in detected asystole in accordance with one or more embodiments willbe discussed. In the case of patients with sudden complete heart blockit is possible for the patient 110 to have p-waves but no QRS complexes.The p-waves, however, may be greater in amplitude than the asystolethreshold 424 so the p-waves can be mistaken as QRS complexes, which mayprevent asystole detection. Furthermore, p-waves can continue at thepatient's normal heart rate for a period of time, so heart block cannotbe detected using heart rate alone. In accordance with one or moreembodiments, complete heart block patients are classified as asystolicbecause complete heart block has no QRS complexes and is non-perfusing.

In some embodiments, WCD system 100 can be configured to detect completeheart block. For example, the WCD system 100 can capture the patient'snormal QRS amplitude, for example during fitting, and can monitors thepatient's QRS complexes for a sudden shift to a lower amplitude. Asudden change or drop to a lower QRS amplitude may be indicative ofcomplete heart block. As shown in plot 500, an ECG signal 510 can havenormal QRS complexes 512 with normal p-waves as shown. ECG signal 510omits t-waves for purposes of discussion. P-waves are normally in therange of about 100 μV to about 200 uV while QRS complexes are normally500 μV to about 3.0 mV in amplitude. In some embodiments, a sudden dropin the amplitude of detected complexes of greater than 50% with anamplitude less than about 200 μV can be determined to be indicative ofcomplete heart block. Thus, in some embodiments, the peak-to-peakamplitude values of the QRS complexes 512 can be measured and monitored,and complete heart block can be detected when the peak-to-peakamplitudes are less than 50% of their normal values and/or when theamplitudes are less than about 200 μV.

In some embodiments a template can be used by WCD system 100 fordetecting complete heart block. For example, a QRS complex template 520can be created during the patient's normal rhythm and stored in a memoryof the WCD system 100. In other embodiments, a p-wave template 522 canbe created and stored in a memory of the WCD system 100. In suchembodiments, the WCD system 100 can be configured to compare detectedQRS complexes to the QRS complex template 520 and/or compare detectedp-waves to the p-wave template 522. The detected morphology of thep-waves during complete heart block should be dramatically differentthan a normal p-wave as reflected by the p-wave template 522.

Plot 502 shows an ECG signal 514 showing a normal QRS complex 512 with anormal p-wave, a low-amplitude QRS complex 516 with a normal p-wave, andthe absence of a QRS complex 520 with an abnormal p-wave 518. Plot 504shows the ECG signal 514, with the low-amplitude QRS complex 516compared with the QRS complex template 520. Plot 504 also shows anabnormal p-wave 518 such as might occur during asystole which iscompared with a normal p-wave template 522. Various techniques can beemployed to compare a received QRS complex with a QRS complex template520 and/or to compare a receive p-wave with a p-wave template 522. Forexample, pattern matching techniques can be used, correlation techniquessuch as a cross-correlation or an auto-correlation wherein a highcorrelation value can indicate a match between the received signal andthe template, and a low correlation value can indicate a sufficientchange to indicate either fine VF for the QRS complex, or to indicateasystole for the p-wave, and so on.

Referring now to FIG. 6 , a diagram of a method to detect asystole in apatient and to discriminate asystole from fine ventricular fibrillation(VF) in accordance with one or more embodiments will be discussed.Although FIG. 6 shows one particular order and number of operations ofmethod 600, it should be noted that method 600 can encompass variousother orders of the operations and/or can include more or feweroperations than shown, and the scope of the disclosed subject matter isnot limited in these respects. Method 600 can be implemented by aprocessor of WCD system 100, for example by processor 1316 as shown inFIG. 13 below, and can be realized a machine readable instructions thatwhen executed result in the operations shown in FIG. 6 . Suchinstructions can be stored in a storage device or memory of WCD system100, such as memory 1320 of FIG. 13 below. Some of the operations ofmethod 600 can be performed in whole or in part by WCD 100, some of theoperations of method 600 can be performed in whole or in part by anotherdevice such as by external monitor 150 of FIG. 1 , and/or some of theoperations of method 600 can be performed in whole or in part by thepatient 110 or by a bystander or some other person such as medicalpractitioner, and so on.

At operation 610, support structure 112 can be fit to patient 110 at aninitial fitting, for example fitting a vest style support structure 112as shown in FIG. 2 and FIG. 3 to patient 110, and normal ECG signals canbe obtained during the fitting. At operation 612, one or more asystolethresholds 424 can be set during the fitting. The asystole thresholdscan be set to a fixed value, or set to a percentage of the peak-to-peakvalue 414 of a normal ECG signal. In some examples, each ECG channel canhave its own unique asystole threshold 424. In some examples, the normalECG signals can be obtained when the patient 110 being fitted is lyingdown or in some similar posture that would be expected during asystole,and the asystole thresholds can be set accordingly. At operation 614,the patient 110 wears support structure 112 and employs WCS system 100to monitor the patient's ECG signals at operation 616 and optionally anyother patient physiological parameter as desired or needed. Suchmonitoring at operation 616 can include monitoring and measuring thepeak-to-peak amplitudes 414 of the patient's QRS complexes.

A determination can be made at operation 618 when the patient's QRSpeak-to-peak amplitudes 414 drop by greater than 50% or somepredetermined amount. If the QRS amplitudes have not droppedsufficiently, then ECG signals may be continued to be monitored atoperation 616. When the QR amplitudes have dropped by the predeterminedamount, a determination can be made at operation 620 whether thepeak-to-peak values 414 are less than the asystole threshold 424. If thepeak-to-peak values 414 are not less than the asystole threshold 424,then it can be determined at operation 622 that fine VF has beendetected, and a process for VF or fine VF can be executed, for examplean analysis as to whether a therapeutic shock 111 should be delivered tothe patient 110. When the peak-to-peak values 414 are determined atoperation 620 to be less than the asystole threshold 424, then it can bedetermined at operation 628 that asystole has been detected, and aprocess for asystole can be executed, for example method 1200 as shownin FIG. 12 and as discussed below can be executed.

Referring now to FIG. 7 , a diagram of a method to detect complete heartblock in a patient in accordance with one or more embodiments will bediscussed. Although FIG. 7 shows one particular order and number ofoperations of method 700, it should be noted that method 700 canencompass various other orders of the operations and/or can include moreor fewer operations than shown, and the scope of the disclosed subjectmatter is not limited in these respects. Method 700 can be implementedby a processor of WCD system 100, for example by processor 1316 as shownin FIG. 13 below, and can be realized a machine readable instructionsthat when executed result in the operations shown in FIG. 7 . Suchinstructions can be stored in a storage device or memory of WCD system100, such as memory 1320 of FIG. 13 below. Some of the operations ofmethod 700 can be performed in whole or in part by WCD 100, some of theoperations of method 700 can be performed in whole or in part by anotherdevice such as by external monitor 150 of FIG. 1 , and/or some of theoperations of method 700 can be performed in whole or in part by thepatient 110 or by a bystander or some other person such as medicalpractitioner, and so on.

At operation 710, support structure 112 can be fit to patient 110 at aninitial fitting, for example fitting a vest style support structure 112as shown in FIG. 2 and FIG. 3 to patient 110, and normal ECG signals canbe obtained during the fitting. At operation 712, a QRS complex template520 can be captured and/or a p-wave template 522 can be captured. Aswith the setting of the asystole thresholds in method 600 above, thetemplates can be captured when the patient 110 is in a selected posturessuch as lying down or in a prone position. At operation 714, the patient110 wears support structure 112 and employs WCS system 100 to monitorthe patient's ECG signals at operation 616 and optionally any otherpatient physiological parameter as desired or needed. Such monitoring atoperation 716 can include monitoring and measuring the peak-to-peakamplitudes 414 of the patient's QRS complexes.

A determination can be made at operation 718 when the patient's QRSpeak-to-peak amplitudes 414 drop by greater than 50% or somepredetermined amount. If the QRS amplitudes have not droppedsufficiently, then ECG signals may be continued to be monitored atoperation 716. In one option, with a sudden drop in the QRS amplitude,and the QRS amplitudes are measured at operation 728 to be below theasystole threshold 424, then complete heart block can be detected, andoperation 724 can be executed as will be discussed in further detailbelow. In another option, with a sudden drop in the QRS amplitude, themonitored ECG signal can be compared at operation 720 to the QRS complextemplate 520 and/or the p-wave template 522. A determination can be madeat operation 722 whether there is a sufficient mismatch between themonitored ECG signal and the QRS complex template 520 and/or the p-wavetemplate 522. If there is not a sufficient mismatch, then then themonitored ECG signal can be analyzed for possible VF at operation 726.When operation 722 determines there is a sufficient mismatch between themonitored ECG signal and the QRS complex template 520 and/or the p-wavetemplate 522, complete heat block can be detected at operation 728, aprocess for complete hear block can be executed, for example method 1200of FIG. 12 as discussed below can be executed.

Referring now to FIG. 8 , a diagram illustrating measurement of arespiration rate of a patient in accordance with one or more embodimentswill be discussed. In the event the ECG signal obtained with WCD system100 appears to show asystole, for example with peak-to-peak amplitude isnear or below the threshold 424, then WCD system 100 can check to see ifthe patient 110 is breathing before rendering a final decision that thepatient 110 is in asystole. In some embodiments, patient respirationscan be detected such as disclosed in U.S. Published Patent ApplicationNo. 20180117299 entitled “WEARABLE CARDIOVERTER DEFIBRILLATOR (WCD)SYSTEM MEASURING PATIENT′S RESPIRATION”, filed on Oct. 25, 2017. Inother embodiments, respirations can be detected using the DC level asdescribed in U.S. Provisional Patent Application 62/911,024 filed Oct.4, 2019 entitled “DC RESPIRATION RATE DETECTOR”. Still other embodimentsmay use other techniques to detect patient respiration. In someembodiments, WCD system 100 may be configured to measure impedancevalues between two ECG electrodes contacting the patient's skin. Plot800 shows detected patient impedance values 810 versus time. Theimpedance values 810 will vary by about +/−1 or 2 ohms as the patientbreathes. The time between consecutive minimum values time T1 and timeT2 can be referred to as the respiration interval 812 from which therespiration rate 814 can be calculated.

In some embodiments, WCD system 110 can include a motion sensor, forexample an accelerometer and/or light emitting devices to sense motionof the patient. These sensors can enhance respiration detectionperformance because an impedance-based respiration detector potentialcan very motion sensitive. WCD patients are ambulatory, so movement ofthe patient is common. Patients who are non-perfusing, however, willtypically not be moving, at least under their own volition, so it can beassumed that if the patient 110 is moving, as evidenced or by anaccelerometer or other motion detector,) then the patient 110 must bebreathing.

It should be noted that different patients can tolerate low heart ratesto different degrees. Some patients may lose consciousness at 40 beatsper minute (BPM) whereas other patients may not lose consciousness untiltheir heart rates fall to 20 BPM. Previous WCDs typically used fixedrate threshold for detecting bradycardia. This approach, however, maycause unnecessary bradycardia alarms in some patients but also may failto alarm for some non-perfusing rhythms. To address this variation ofthe effect of bradycardia on different patients, patient respiration maybe used in conjunction with heart rate to detect whether the patient 110is experiencing bradycardia.

Referring now to FIG. 9 , a diagram of detection of bradycardia in apatient using a conditional heart rate zone in combination with patientrespiration in accordance with one or more embodiments will bediscussed. As shown in FIG. 9 , respiration detection can be used indetermining whether bradycardia is perfusing or non-perfusing. Chart 900shows patient heart rates in beats per minute (BPM). A conditionalthreshold 910 can be set at a first heart rate, for example 40 BPM. Anabsolute threshold 912 can be set at a second heart rate, for example 20BPM. Heart rates above the conditional threshold 910 can be consideredto be in the non-bradycardia zone 914 such that patient 110 is notexperiencing bradycardia. Heart rates below the absolute threshold 912can be considered to be in the bradycardia zone 918. Heart rates belowthe conditional threshold 910 but above the absolute threshold 912 canbe considered to be the conditional heart rate zone 916. Heart rates inthe conditional heart rate zone 916 will not trigger a bradycardia alarmif patient respiration is detected. If no respiration is detected in theconditional heart rate zone 918, then a bradycardia alarm will betriggered. When the patient's heart rate falls below the absolutethreshold, then the bradycardia alarm will be triggered regardless ofthe presence or absence of patient respirations.

Referring now to FIG. 10 , a diagram of detection of asystole in apatient using a conditional amplitude zone in combination with patientrespiration in accordance with one or more embodiments will bediscussed. As shown in FIG. 10 , respiration detection can also beuseful in detecting complete heart block. In some embodiments, this isin addition to detection of bradycardia, for example as discussed withrespect to FIG. 9 , above. While bradycardia detection can use aconditional heart rate threshold, in some embodiments asystole detectioncan utilize a conditional amplitude threshold. For example, chart 900shows peak-to-peak QRS complex amplitude in volts. A conditionalthreshold 1010 can be set at a first amplitude, for example 200 μV. Anabsolute threshold 1012 can be set at a second amplitude, for example100 μV. Signals having amplitudes above the conditional threshold 1010can be considered to be in the non-asystole zone 1014 such that patient110 is not experiencing asystole. Signals having amplitudes below theabsolute threshold 1012 can be considered to be in the asystole zone1018 and definitely classified as asystole. Signals having amplitudesbelow the conditional threshold 1010 but above the absolute threshold1012 can be considered to be the conditional amplitude zone 1016. Signalamplitudes in the conditional amplitude zone 1016 will not trigger anasystole alarm if patient respiration is detected. If no respiration isdetected in the conditional amplitude zone 918, then an asystole alarmwill be triggered. When the patient's amplitude falls below the absolutethreshold, then the asystole alarm will be triggered regardless of thepresence or absence of patient respirations.

Such an arrangement of using respiration in combination with signalamplitude can assist with detection of complete heart block becausep-waves would tend to fall in the conditional amplitude zone 016. Thus,when asystole occurs where there is no QRS complex but a p-wave maystill be present, the amplitude of the p-wave can be in the conditionalamplitude zone 1016. In this situation, the absence of patientrespiration can confirm asystole.

Referring now to FIG. 11 , a diagram of discrimination between asystoleand fine ventricular tachycardia (VT) or ventricular fibrillation (VF)using a conditional amplitude zone in accordance with one or moreembodiments will be discussed. Chart 1100 shows a conditional amplitudethreshold 1110, an absolute amplitude threshold 1112, and a conditionalamplitude zone 1116 for peak-to-peak QRS complex signals similar to thatshown in FIG. 10 . Within conditional amplitude zone 1116, other factorsmay be used to distinguish fine VF from complete heart block. In someembodiments, the patient's heart rate and QRS complex width can be usedto detect VT or VF as described in U.S. Pat. No. 10,105,547 entitled“WEARABLE CARDIOVERTER DEFIBRILLATOR (WCD) CAUSING PATIENT'S QRS WIDTHTO BE PLOTTED AGAINST THE HEART RATE”. In such embodiments, rhythms canbe classified as VT/F in zone 1114 when VT/VF criteria are met, and adetected rhythm that meets the VT/VF criteria and falls in theconditional amplitude zone 1116 can be classified as fine VT/VF. If theheart rate falls below the VT rate threshold, however, and the amplitudeis in the conditional amplitude zone 1116, then such rhythms in theconditional amplitude zone would be classified as asystole. In anyevent, amplitudes below absolute threshold 1112 in asystole zone 1118will be classified as asystole.

Referring now to FIG. 12 , a method to address asystole or bradycardiain a patient using a wearable cardioverter defibrillator (WCD) inaccordance with one or more embodiments will be discussed. Patientsexperiencing asystole or severe bradycardia may quickly loseconsciousness and may die if prompt treatment is not provided. Method1200 may be executed when asystole or bradycardia conditions are met.Asystole or bradycardia can be detected at operation 1210. To help thepatient 110, WCD system 100 can issue prompts at operation 1212 to anybystander to call EMS and/or to provide CPR until help arrives. Forexample, the system may be configured to issue voice prompts tobystanders to intervene as described in U.S. Pat. No. 10,426,964entitled “WEARABLE CARDIAC DEFIBRILLATOR SYSTEM EMITTING CPR PROMPTS FORBYSTANDER”. In other embodiments, WCD 100 can be configured tooptionally provide temporary external pacing to patient 110 at operation1214 similar to that described in U.S. Pat. No. 8,838,236 entitled“WEARABLE CARDIAC DEFIBRILLATOR SYSTEM WITH ANTI-BRADYARRHYTHMIA PACING& METHODS” to bridge the patient over until EMS arrives.

Referring now to FIG. 13 , a diagram of the elements of a wearablecardioverter defibrillator (WCD) using an external monitor to provideadditional patient physiological parameter information to the WCD inaccordance with one or more embodiments will be discussed. The WCD 100shown in FIG. 13 incorporates one or more of the features discussedherein to detect asystole and/or bradycardia. In some embodiments, WCDsystem 100 can include an external monitor 150 that can comprise pulsesensor or non-invasive blood pressure measurement capability. WCD system100 can be configured to also use the data from one or more of thesesensors to determine if the patient 110 is perfusing.

The ECG electrodes, (E1) 122, (E2) 124, (E3) 126, and (E4) 128, cancomprise silver or silver plated copper electrodes that “dry” attach tothe skin of the patient 110. The ECG electrodes provide ECG/QRS data topreamplifier 1310 in hub/monitoring device 114. The preamplifier 132 mayhave a wide dynamic range at its input, for example +/−1.1 V which ismuch larger than the amplitude of the ECG signals which are about 1 mV.The preamplifier 1310 includes analog-to-digital converters (ADCs) 1312to convert the ECG signals into a digital format. A right-leg drive(RLD) electrode 130 can be used to provide a common mode signal so thatthe ECG signal from the ECG electrodes can be provided to preamplifier1310 as differential signals. The digital ECG signals are provided fromthe preamplifier 1310 eventually to the main processor 1316 of monitor150 via an isolation barrier 1314 which operates to electrically isolatethe preamplifier 1310 and the ECG signals from the rest of the circuitryof WCD 100.

The processor 1316 processes the digital ECG/QRS data received from thepreamplifier 1310 with one or more digital filters 1318. Since thepreamplifier 1312 has a wide dynamic range that is much wider than theamplitude range of the ECG signals, digital filters 1318 be utilized toprocess the ECG/QRS data without concern for clipping the incomingsignals. One of the digital filters 1318 can include a matched filter tofacilitate identification of QRS pulses in the incoming data stream. Thewide dynamic range of the preamplifier 1310 allows at least most of theECG filtering to happen in software without the signal being clipped.Digital filters 1318 can be very effective at removing artifacts fromthe ECG/QRS data and may contribute to the enhanced false positiveperformance, that is a lower false positive rate, of the WCD 100according to embodiments as described herein.

The processor 1318 can apply the rhythm analysis algorithm (RAA) storedin memory 1320 using QRS width information and heart rate data extractedfrom the digital ECG data using segment-based processing analysis and/orQRS width versus heart rate 7 to make a shock or no-shock determinationfor VT and/or VF. The RAA receives the digitized ECG signal andcalculates the heart rate and QRS width for each segment. The digitizedECG signal is passed over the isolation barrier 1314, and the heart rateis derived from the digitized ECG signal. The heart rate and QRS widthare used for making a shock/no-shock decision for each segment, whichthen can lead to an alarm and a shock. In the event a shockable event isidentified, the processor 1316 will open a tachycardia episode to startthe shock process. Unless the patient 110 provides a patient responseusing the alert/stop button 120 or other user interface to send a stopshock signal to the processor 1316 to intervene before the shock isapplied, the processor 1318 can send a shock signal to the high voltagesubsystem 1322 in the carry pack/defibrillator 118 which will apply adefibrillation voltage across the defib front electrode 104 and thedefib back electrode 108 to apply one or more therapeutic shocks untilthere is no longer any shockable event (VT or VF) or until the energy inthe high voltage subsystem 1322 is depleted.

Although the claimed subject matter has been described with a certaindegree of particularity, it should be recognized that elements thereofmay be altered by persons skilled in the art without departing from thespirit and/or scope of claimed subject matter. It is believed that thesubject matter pertaining to asystole and complete heart block detectionand many of its attendant utilities will be understood by the forgoingdescription, and it will be apparent that various changes may be made inthe form, construction and/or arrangement of the components thereofwithout departing from the scope and/or spirit of the claimed subjectmatter or without sacrificing all of its material advantages, the formherein before described being merely an explanatory embodiment thereof,and/or further without providing substantial change thereto. It is theintention of the claims to encompass and/or include such changes.

What is claimed is:
 1. An apparatus of a wearable cardioverterdefibrillator (WCD) system, comprising: a support structure wearable bya patient; a plurality of electrocardiogram (ECG) electrodes capable ofbeing applied to the skin of the patient to obtain an ECG signal; aprocessor to receive and analyze the ECG signal of the patient, whereinthe processor is configured to monitor four or more channels of the ECGsignal; and a high voltage subsystem coupled with defibrillationelectrodes configured to be coupled with patient, wherein the processoris configured to cause the high voltage subsystem to apply a therapeuticshock to the patient through the defibrillation electrodes in responseto a shockable event detected by the processor from the ECG signal;wherein the processor is further configured to: measure a peak-to-peakamplitude of QRS complexes of the ECG signal; and detecting asystole inthe patient when the peak-to-peak amplitude of one or more QRS complexesis less than an asystole threshold; and wherein a unique asystolethreshold is set for each of the four or more channels.
 2. The apparatusof claim 1, wherein the unique asystole threshold of at least one of thefour or more channels is set to a fixed value.
 3. The apparatus of claim2, wherein the fixed value ranges from about 100 microvolts to about 200microvolts.
 4. The apparatus of claim 1, wherein the unique asystolethreshold of at least one of the four or more channels is set to apercentage of a peak-to-peak amplitude of a normal QRS complex of thepatient.
 5. The apparatus of claim 1, wherein the processor is furtherconfigured to: detect respiration of the patient; and determine that thepatient is in asystole when the peak-to-peak amplitude of one or more ofthe QRS complexes is lower than a unique conditional threshold andhigher than an absolute threshold for at least one of the four or morechannels, and when no patient respiration is detected.
 6. The apparatusof claim 1, wherein asystole is detected only when the peak-to-peakamplitudes of QRS complexes in all four channels falls below the uniqueasystole threshold for each of the four or more channels.
 7. Anapparatus of a wearable cardioverter defibrillator (WCD) system,comprising: a support structure wearable by a patient; a plurality ofelectrocardiogram (ECG) electrodes capable of being applied to the skinof the patient to obtain an ECG signal; a processor to receive andanalyze the ECG signal of the patient, wherein the processor isconfigured to monitor four or more channels of the ECG signal; and ahigh voltage subsystem coupled with defibrillation electrodes configuredto be coupled with patient, wherein the processor is configured to causethe high voltage subsystem to apply a therapeutic shock to the patientthrough the defibrillation electrodes in response to a shockable eventdetected by the processor from the ECG signal; wherein the processor isfurther configured to: measure a peak-to-peak amplitude of QRS complexesof the ECG signal; detect respiration of the patient; and detectasystole in the patient when the peak-to-peak amplitude of one or moreof the QRS complexes is lower than a conditional asystole threshold andhigher than an absolute asystole threshold, and when no patientrespiration is detected.
 8. The apparatus of claim 7, wherein theconditional asystole threshold is set to a fixed value.
 9. The apparatusof claim 8, wherein the fixed value ranges from about 100 microvolts toabout 200 microvolts.
 10. The apparatus of claim 7, wherein theconditional asystole threshold is set to a percentage of a peak-to-peakamplitude of a normal QRS complex of the patient.
 11. The apparatus ofclaim 7, wherein a unique conditional asystole threshold is set for eachof the four or more channels.
 12. The apparatus of claim 7, whereinasystole is detected only when the peak-to-peak amplitudes of QRScomplexes in each of the four or more of the channels falls below theconditional asystole threshold.
 13. An apparatus of a wearablecardioverter defibrillator (WCD) system, comprising: a support structurewearable by a patient; a plurality of electrocardiogram (ECG) electrodescapable of being applied to the skin of the patient to obtain an ECGsignal; a processor to receive and analyze the ECG signal of thepatient, wherein the processor is configured to monitor four or morechannels of the ECG signal; and a high voltage subsystem coupled withdefibrillation electrodes configured to be coupled with patient, whereinthe processor is configured to cause the high voltage subsystem to applya therapeutic shock to the patient through the defibrillation electrodesin response to a shockable event detected by the processor from the ECGsignal; wherein the processor is further configured to: measure apeak-to-peak amplitude of QRS complexes of the ECG signal; and detectingasystole in the patient when the peak-to-peak amplitude of one or moreQRS complexes is less than an asystole threshold; and wherein asystoleis detected only when the peak-to-peak amplitudes of QRS complexes ineach of the four or more channels falls below the asystole threshold.14. The apparatus of claim 13, wherein the asystole threshold is set toa fixed value.
 15. The apparatus of claim 14, wherein the fixed valueranges from about 100 microvolts to about 200 microvolts.
 16. Theapparatus of claim 13, wherein the asystole threshold is set to apercentage of a peak-to-peak amplitude of a normal QRS complex of thepatient.
 17. The apparatus of claim 13, wherein a unique asystolethreshold is set for each of the four or more channels.
 18. Theapparatus of claim 13, wherein the processor is further configured to:detect respiration of the patient; and determine that the patient is inasystole when the peak-to-peak amplitude of one or more of the QRScomplexes is lower than a conditional systole threshold and higher thanan absolute asystole threshold, and when no patient respiration isdetected.